Sex tips please ?!

My boyfriend is 6’4 at 180lbs and I’m 5’4 at 215lbs. He’s asked me if I could be on top but I don’t exactly know what I’m doing. I’m nervous that my fat will get in the way or it will be a turn off. I feel like I’m squishing him 🌚 He specifically asked since I didn’t know how to ride if I’d just go up & down and all I can think as a chubby girl, is if I’m going to hurt him or it won’t even feel good lmao. I’m also having problems climaxing in the first place. He is always up for anything i suggest & everything usually feels great yet … nothing. Any advice would help please.